The present invention relates generally to optical transmission and, more particularly, to an optical power equalizer capable of equalizing the optical power of optical signals in a passive optical network.
The increasing demand for faster and higher capacity information processing and transmission has accelerated the development and research in optical fiber networks and systems. Information may be transported through optical systems in audio, video, data, or other signal formats analogous to electrical systems. Furthermore, optical systems may be used in telephone, cable television, local area network (“LAN”) and wide area network (“WAN”) systems as well as other communication systems. Optical systems may also offer various communication services such as voice over internet protocol (“VoIP”) and internet protocol television (“IPTV”) services in a fiber-to-the-X (“FTTX”) architecture, including fiber-to-the-home (“FTTH”), fiber-to-the-premise (“FTTP”), fiber-to-the-curb (“FTTC”) or the like.
A passive optical network (“PON”) is one of optical network systems used for the FTTX architecture for introducing optical communications. FIG. 1 is a block diagram of a conventional PON 10. Referring to FIG. 1, the PON 10 includes an optical line termination (“OLT”) 11, an optical splitter 12 and a plurality of optical network units (“ONUs”) 13-1 to 13-N. Each of the ONUs 13-1 to 13-N transmits optical signals upstream to the OLT 11 through the optical splitter 12. However, since the distance between the OLT 11 and the ONUs 13-1 to 13-N may be different from each other, optical signals 14-1 to 14-N may reach the OLT 11 with different optical powers due to, for example, signal path attenuation. The different power levels may disadvantageously result in an incorrect detection of the optical signals at the OLT 11. Generally, a burst mode receiver (not shown) may be provided in the OLT 11 to equalize the optical powers of the optical signals. The burst mode receiver is required to detect a relatively wide range of powers, for example, 21 dB to 24 dB, and support dynamic adjustment of decision threshold values, which may complicate the OLT structure and reduce the bandwidth efficiency.
It may be therefore desirable to have an optical power equalizer that is able to equalize the optical power of optical signals in a passive optical network. It may be also desirable to have an optical power equalizer that is able to cost-efficiently equalize optical signals at an OLT side.